The present invention relates to an ink jet recording apparatus used for printing.
For example, with conventional ink jet recording apparatuses used for color printing, the ink drops of four color inks, i.e., yellow, magenta, cyan, and black are ejected through orifices in the ink jet head. The respective color ink drops adhere to the print medium one over the other, forming a dot of a desired color.
The ink jet head has an ink drop generating mechanism made of, for example, a heater or a piezoelectric material. The ink drop generating mechanism is driven in accordance with color information to eject the corresponding color ink drops. Further, each pixel is in the form of, for example, a 4-by-4 dot matrix and the gradation of a printed image may be achieved by varying print density on a pixel-by-pixel basis.
The ink drops are ejected at a timing in accordance with the print resolution (e.g., 300 dpi) of the ink jet recording apparatus. The amount of ink of each of the ejected ink drops is in accordance with the gradation of the print data.
However, the ink drops ejected from the moving ink jet head travel toward the print medium at different initial velocities depending on the amount of ink contained in the ink drop. Therefore, the aforementioned prior art ink jet recording apparatus suffers from a drawback that it is difficult to print an image with the respective color dots accurately registered on the print medium. Inaccurate registration results in ink-spread, misregistration of color inks on each dot location, and deviation of printed dots from correct positions, all of which are the sources of poor print quality. Effecting gradation of color on a pixel-by-pixel basis lowers the resolution of the ink jet recording apparatus by the size of a pixel.
In one method of accurately aiming color ink drops at the same dot location on the print medium that has been proposed, two or three ink drops are deposited consecutively one over the other at the same dot location on the print medium. Each of the color ink drops has the same amount of ink as an ink drop required for printing a full sized single color-dot. Thus, a large amount of ink adhering to one dot location requires a longer time for the ink to dry, resulting in a problem such as ink spread.